This application claims the priority of German application 101 30 906.6, filed Jun. 27, 2001, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a motor vehicle transmission with a parking lock mechanism.
A parking lock system for an automatic transmission with a hydraulic torque converter is known from LECHNER, G., Fahrzeuggetriebe [Vehicle Transmissions], Springer-Verlag, 1994, pages 232 to 233. Such a parking lock system with positive interlock must secure the vehicle reliably against rolling away, even on a downward or upward gradient, when the parking brake is not actuated. This also has to be ensured, where possible, when, with the vehicle stationary, direct actuation by means of a parking-lock wheel-tooth/pawl-tooth position is not possible, but the stopped vehicle could subsequently move independently. The latched parking lock mechanism must likewise also be capable of being released again without difficulty.
German patent publications DE 195 33 141 C1 and DE 100 29 628 A1 already disclose parking lock mechanisms which make frictional connections such as those of the invention.
The object of the invention is to provide a convenient motor vehicle transmission with a parking lock mechanism.
The object referred to is advantageously achieved, according to the invention, by a motor vehicle transmission with a parking lock mechanism including a friction brake by which a frictional connection can be made between a transmission case and a transmission shaft, with the friction brake being engageable and disengageable.
One advantage of the invention is that engagement operations of the parking lock mechanism can be controlled continuously. In this case, the required locking moment is generated with the aid of a frictional parking lock mechanism. It is thus advantageously possible to eliminate the drive-train stress-relief bump by means of a regulated operation of disengaging the parking lock mechanism. This contributes to an increased improvement in comfort.
In the overall structure of this system, with what is known as xe2x80x9cshift by wirexe2x80x9d, the release of the parking lock mechanism no longer requires any additional effort which depends directly proportionally on the downward or the upward gradient when vehicle-side manual actuation is used. It is possible, in this connection, to sense the vehicle speed more accurately, so that the frictional parking lock mechanism or a friction brake is protected against unnecessary wear or unnecessary destruction as a result of more accurate control/regulation. Thus, in the case of a P-R-N-D manual selector lever for selecting the driving range, it is possible, even at relatively high limit speeds, to allow a shift from N to R, for example during manoeuvring. A further shift from R to P is possible on the selector lever, but is not allowed within the transmission by the shift logics.
According to a particularly advantageous refinement of the invention, force amplification as a result of the cone angle is utilized. Since the shift force has to be applied by the hydraulic system, the power losses in the hydraulic system of the motor vehicle transmission with a friction brake are lower in the embodiment according to the invention than, for example, when multiple-disc clutches are used.
In refinements of the invention providing a further improvement in the overall efficiency of the motor vehicle transmission, a force accumulator which exerts the holding force necessary for self-locking makes it possible to compensate wear and manufacturing tolerances in a particularly advantageous way.
In another refinement of the invention, particularly convenient control of the engagement and disengagement of the parking lock mechanism becomes possible.
Further advantages of the invention may be gathered from various claims, the description and the drawings.